Forge

Overview
The Forge is a mid-tier building that allows players to craft metal tools, armor and weaponry, of the iron and steel tier (Tiers 2 and 3). The Forge is an extremely popular building, and any decent tribe is almost guaranteed to have a forge. A small furnace inside allows for refining of up to 8 ores total; some may also use it to cook smaller foods.

If you find a tribe with a forge present, along with a lack of a Smeltery, then it's very likely that they won't have Mithril or Bluesteel items.